A mounting unit for rotatably and captively fastening the fastening eyelet of a belt buckle (i.e. the mounting part) to a part of the interior (i.e. the component) of a commercial vehicle is generally known from commercial vehicles by DaimlerChrysler AG. The mounting unit includes a screw including a head, a shank portion and a threaded portion including a thread. The shank portion is located in a region between the head and the threaded portion. Furthermore, the mounting unit includes a washer and two mounting discs. A necessary element of the mounting unit furthermore is the mounting part without which there would be no mounting unit, but instead only five separate elements. For mounting the mounting unit, at first the washer is pushed over the shank portion of the screw. The washer includes a bore the inner diameter of which is greater than the outer diameter of the shank portion and smaller than the outer diameter of the head of the screw such that the washer contacts the contact surface of the head. Afterwards, the mounting part with its bore is moved over the screw until the mounting part contacts the washer. The inner diameter of the bore of the mounting part is also greater than the outer diameter of the shank portion of the screw. Subsequently, the first mounting disc is pushed over the screw. The first mounting disc has a stepped design in a way that it includes a first section the outer diameter of which is slightly smaller than the inner diameter of the bore of the mounting part. This first section is pushed into the bore of the mounting part. The second section has a greater outer diameter which thus contacts the outer surface of the mounting part. The captive connection of the mounting unit is realized by the second mounting disc. The second mounting disc at its inner circumference includes radial slots between which tabs are formed. During assembly of the second mounting disc, these tabs engage into the threads of the thread, and the second mounting disc is screwed onto the thread of the screw or pressed or pushed over the thread when there is a respective elastic design until it contacts the first mounting disc. In this way, it clamps the mounting part between the first mounting disc and the washer. By respectively choosing the materials, it is ensured that the required radial clearance or play between the mounting part and the mounting disc does not lead to rattle noises. The known mounting unit has a comparatively complicated design, and in addition to the screw and the mounting element, it requires three separate elements. The captive arrangement of the mounting unit is not attained until the mounting element is mounted.
Furthermore, it is known in the prior art in the automobile industry to fasten the fastening eyelet of a belt buckle (i.e. the mounting element) of an automobile or a truck to a part of the interior (i.e. the component) of the automobile and of the truck, respectively, in a rotatable way. For this purpose, no mounting unit is used. The mounting element is connected to the component by screwing using a screw and a separate resilient wave washer. The screw includes a head, a shank portion and a threaded portion including a thread. The shank portion is located in a region between the head and the threaded portion. The wave washer includes a bore having an inner diameter being greater than the outer diameter of the shank portion. At first, the wave washer is pushed upon the screw until it approximately contacts the head of the screw. The wave washer is not fixedly connected to the screw in any way. Afterwards, the fastening eyelet of the belt buckle is also pushed over the screw. In this loose position of the three elements, the screw is screwed into a bore of the component until the shoulder of the screw limiting the shank portion in a direction towards the threaded portion firmly contacts the component. The wave washer with its one side contacts the component and with its other side contacts the fastening eyelet such that the fastening eyelet is clamped. This means that the fastening eyelet is fixed between the wave washer and the head of the screw to be rotatable, but not to be movable in the direction of the axis of the screw. The elastic force of the wave washer serves to prevent rattle noises caused by the axial clearance or play of the fastening eyelet.
A mounting unit for rotatably and captively fastening a screw to a mounting part is known from German patent application No. DE 100 55 405 A1, corresponding to U.S. Pat. No. 6,626,626 B2. The assembly unit includes a screw including a head, a shank portion and a threaded portion including a thread. The shank portion is located in a region between the head and the threaded portion. The mounting unit furthermore includes a mounting ring. The mounting ring is made of plastic, and it is designed to be elastic. Furthermore, there is a mounting part including a bore and a component including a bore with an inner thread being associated with the thread of the screw. Due to the non-circular cross-section of the bore of the mounting part, the mounting ring is not rotatably arranged in the mounting part. Furthermore, due to a collar and an expanding rib, the mounting ring is arranged to be not movable with respect to the mounting part. The mounting ring has an inner diameter which is smaller than the outer diameter of the thread of the threaded portion of the screw. The mounting ring in the position of the mounting unit not being fully screwed into the component (see FIG. 1) is located in the region of the threaded portion of the screw. Due to the respective sizes of the inner diameter of the mounting ring and of the outer diameter and of the core diameter of the thread of the threaded portion of the screw, respectively, the mounting ring can be moved with respect to the screw, and the screw can be screwed or pressed into the mounting ring, respectively, due to elastic or elastic and plastic deformation. The mounting ring is not located in the region of the shank portion of the screw until assembly of the mounting part at the component has been completed, meaning when the screw has been fully screwed into the component (see FIG. 2). In this position, the mounting ring has already fulfilled its function and is no longer required in this sense. It is neither rotatable nor movable with respect to the mounting part. The mounting ring fulfills its actual function in connection with the threaded portion of the screw (see FIG. 1). This prior art reference does not relate to fixing a mounting part at a component in a way that the mounting part in its position connected to the component by screwing can be rotated with respect to the component.
Another mounting unit for rotatably and captively fastening a screw to a mounting unit is known from U.S. Pat. No. 3,156,281. The mounting unit includes a screw including a head, a shank portion and a threaded portion including a thread. A shank portion is located in a region between the head and the threaded portion. Furthermore, the mounting unit includes a mounting ring. The mounting ring is especially made of elastic spring steel. In its position in which the mounting unit is not connected to the mounting part (see FIG. 3), the mounting ring is arranged in the region of the shank of the screw to be freely movable and rotatable. The combination of the screw and the mounting ring is then introduced into the mounting part from above (see FIG. 4). The mounting ring at its outer circumference includes protruding elastic elements which serve to fasten the mounting ring in the opening of the mounting part to a certain extent. In contrast, the screw is freely rotatable with respect to the mounting ring, and it can be freely moved with respect to the mounting part and the mounting ring within the distance between the head of the screw and the end of the threaded portion facing the head of the screw. This prior art reference does not relate to fixing a mounting part at a component in a way that the mounting part in its position connected to the component by screwing can be rotated with respect to the component.